Alternating-current transformer



Mal'Ch 24, 1931. F- BEDELL ALTERNATING CURRENT TRANSFORMER Filed Oct. 18, 1928 ATTORNEY Patented Mar. 24, 1931 UNITED STATES FREDERICK BEDELL, or ITHACA, Nnw Yoan ALTERNATING-CURRCENT TRANSFORMER Application led October 18, 1928. Serial No. 313,357.

My invention relates to improvements in alternating Acurrent transformers, whereby the voltage delivered to secondary receiving devices is independent, or substantially independent, of variations in primary supply voltage. Many types of receiving devices require for best operation a more constant voltage supply than can usually be obtained from a generator or from the distribution lines of a power system.

'An object of my invention is to provide transformers for operating such devices at constant voltage and hence also at constant current, irrespective of variations in the voltage of a supply line or generator. The secqondary receiver may consist of a single device, or several devices (such as the filaments of lamps or radio tubes) arranged either in series, as in Fig. 1,*.or in multiple, as in Fig. 2, or in series-multiple. While such devices may from time to time be changed or adjusted, if desired, the purpose of my invention is not to maintain the secondary voltage or current constant, irrespective of such changes or adjustments, but after such changes or adjustments, if any, are made, to

maintain 'constant both secondary current and secondary voltage while primary current and voltage are both varying.

My invention consists in the disposition of the secondary winding of the transformer with respect to the magnetic circuit and to the primary winding, so that only part of the magnetic Vflux set up by the primary winding (hereafter referred to as the primary) passes through or links with the secondary winding (hereafter referred to as the secondary) In order to accomplish this, the -secondary is--displaced with respect to 49 the primary so that, on account of magnetic leakage, it 1s loosely coupled therewith, This is contrary to the usual practice in the -construction of transformers for power and light, in which the primary and secondary are placed closely together in such a way that l they are closely coupled, magnetic leakage being made a minimum.

My invention consists, further, in propor.

tioning the iron in that part of the magnetic 50 circuit which conducts the magnetic flux through the windings of the secondary, so that, under normal operation, such iron is at high magnetic saturation. This may be accomplished by placing the primary on one limb of the magnetic circuit and the secondary on another limb the cross-section of which is so reduced that the iron is operated, magnetically, above the knee of the satura' tion curve. In this case the increase in magnetizing ampere turns, resulting from an lncrease in primary voltage and current, is accompanied by a nearly proportional increase in the reluctance'of the iron, which is already saturated. A considerable increase or decrease) in primary voltage and current may thus occur with only a small increase (or decrease) in secondary flux and hence 1n secondary voltage and current.

My invention consists further in the provision of a leakage path for the surplus magnetic flux set up by the primary which does not pass through or link with the secondary, such leakage path being preferably in part through airor other non-magnetic material,

the magnetic reluctance of which is independent of saturation. As the total flux 1s increased, therefore, duefto an increase in pri'- mary voltage and so 1n magnetizmgI ampere turns, av greater proportion of this total flux passes through this leakage path; the increase in the flux threading the secondary, and,

hence, the increase'in the secondary voltage,

is, therefore relatively small.

Finally, to compensate for this relatively `small increase in secondary voltage with increase in primary voltage, my invention includes a compensating winding, displaced with respect to the secondary' and connected differentially therewith. The voltage of this .compensating winding (which is less than the secondary voltage) 'is thus subtracted from the voltage of the secondary. To carry out this part of my invention, the compensat ing winding is displaced, with reference to the secondary, so as to be on a part of the magnetic circuit of lower magnetic saturation, preferably below the knee of. saturation. A change in primary voltage thus makes a corresponding change in thevoltage of the compensating winding, which has such a number of turns relative to the number of turns in the lsecon ary) that, when the voltage of the compensating winding is subtracted from the volta e of the secondary, the resultant voltage elivered to the secondary is practically constant. v v

My invention is illustrated in the accompanying drawings forming part of this application, in which:

Figure of my invention.

Figure'2 is a modiiied form thereof. Figure 3 is a view of another modified form in which the. compensating winding is energized by a separate transformer.

Referring now particularly to Fig. 1 I have shown therein the closed magnetic vcircuit of a transformer including limbs A1 and B1.

" On the limb A1 is the primary winding P1,

' S1. A compensating winding C1 which is connected by the conductor p1 to the lines leading from some source of current such as the generator G1. The limb B1 has the secondary winding S1, which, as will be noted, is displaced with respect to the primary winding so as to be loosely coupled therewith, and hence to be threaded with only such part of the magnetic f iux produced by the primary winding as passes through the limb B1. In this figure the dotted line L1 indica-tes a leakage path taken by the surplus magnetic iiux produced by the primary winding P1 which does not thread the secondary with reference to the secondary winding S1 is provided, this winding being of lo'wer voltage than S1 and being connected diierentially thereto so that its voltage is subtracted from the voltage of S1'. At R1 I have shown receiving devices which in the present instance are i connected in series.

In Figure 2 I-have shown a construction in which the limb B2 which `passes through the secondary winding S1 isof smaller cross section and of higher magnetic saturation than the limb A1 upon which the primary P2 is wound. The reluctance of the limb B2 is thus increased.' lFurthermore the leakage path Leis shortened, due to the projecting parts V1 of the magnetic circuit -and the reluctance of the leakage path is thus decreased. An air gap, however', is retained so that the reluctance of the leakage path is practically independent lof saturatio Figu windings may be common to'theother windin l lthough I prefer that the compensating winding forms part ofthe 1 represents a general embodimentv displaced re 2 vlikewise shows a modification in -which some of the turns of the primary l?2 v and of the compensating winding G2 are common. Any or all of the turns of one of these magnetic leakage so that the voltage of the compensating winding varies practically in proportion to the primary voltage. Thus in Fig. 3 I have shown a transfrmer T1, which is connected with the primary winding S11.

I am aware that the prior art may disclose devices having paths for magneticleakage and possibly magnetic circuits of high saturation in the secondary, for the purpose of holding either the secondary current, or the sec-l ondary voltage const-ant (but not both) when the load is changed, the primary current or the primary voltage being constant. The purpose of the present invention however is different. Neither the primar voltage nor the current is constant, but oth the secondary voltage and current is held constant by the present invention for constant arrangement of receiving devices.

1. A transformer consisting of a magnetic circuit, a primary Wound on part of said circuit witli low magnetic saturation, a secondary wound on part of said circuit with a relatively high magnetic saturation, and a compensating winding comprising part of the primary winding, and being connected differently in series with said secondary winding and with the load.

2. In a transformer, a ma etic circuit with varying cross-section, a primary wound on a part of said magnetic circuit with relatively large cross section, a secondary wound on part of said magnetic circuit with relatively small cross section, and a compensating winding comprising part of the primary winding and connecteddi'erentially in series viti said secondary winding and with the 3. In a transformer, a magnetic circuit consisting of one portion upon which is wound a primary coil, a second rtion of high magnetic saturation and variable reluctance upon which is wound a secondary coil, and a third 1 sating coil comprising (part of the primary Winding and connected erentially in series fvitli said secondary winding and with the i4. In a transforming device,-a" magnetic circuit, a primary) wound on vone portion of the circuit, a secondary displaced from said primary on another portion of the circuit and a compensating winding comprising part of the` primary winding and connected differentially in series with said secondary windg and with the load.

FREDERICK BEDELL..

transformer, said transformer having little 

